Predictive diagnostics systems and methods using vacuum pressure control valves

ABSTRACT

Calibration of a valve in a vacuum system and providing a diagnostic indication in the vacuum system using the calibration includes measuring conductance of the valve as a function of angular valve position and generating a conductance calibration map or function for use during operation of the valve. An actual angular valve position is set based on the received set point angular valve position and a difference between the measured valve conductance and a predefined metric of conductance versus angular valve position. An actual system conductance and a difference between the actual system conductance and a reference system conductance for the system are determined. The diagnostic indication of a fault in the system is generated based on the actual angular valve position of the valve and the difference between the actual system conductance and the reference system conductance for the system.

RELATED APPLICATION

This application is related to and claims priority to U.S. ProvisionalPatent Application No. 62/333,989, filed on May 10, 2016, the entirecontents of which are incorporated herein by reference.

BACKGROUND 1. Technical Field

The present disclosure is related to vacuum pressure control valves,and, in particular, to systems and methods using predictive diagnosticsin connection with vacuum pressure control valves.

2. Discussion of Related Art

A typical vacuum-based processing system, such as, for example, asemiconductor processing system, often includes one or more valves and avacuum pump positioned downstream of a processing chamber to control theflow of fluids through the chamber. These fluids flowing through thechamber can include, for example, reactive gases used to etch or coat asemiconductor wafer in the chamber. The vacuum pump creates a pressuredifference between a location upstream of the valve and a locationdownstream of the valve. Flow through the chamber is controlled byvarying the conductance of the valve by changing the degree to which thevalve is open/closed.

Butterfly valves are commonly used in vacuum pressure control systems,such as those employed in semiconductor fabrication systems. A butterflyvalve, or “flapper valve,” typically includes a thin flapper coaxiallydisposed within a passageway through the valve housing. The flapper issecured to the valve assembly by a rotatable valve shaft extendinglaterally across the passageway. Rotation of the valve shaft controlsthe position of the flapper with respect to the valve housing. Theconductance of a butterfly valve is controlled by varying the positionof the flapper between open (100% open) and closed (0% open) positions.

In such processing systems, various factors can cause degradation insystem performance over time. For example, in deposition tools,deposition by-products can build up in the valve and/or in the pumpingline. This build-up can change the fluid conductance of one or morecomponents of the vacuum system. Also, a flexible seal between theflapper and the valve body can wear over time, which can also alter theconductance performance of the vacuum system, and, in particular, thevalve.

SUMMARY

According to a first aspect, a method for calibrating a valve in avacuum system is provided. According to the method, conductance of thevalve as a function of angular valve position is measured. A conductancemap or function for the valve is determined by comparing the measuredvalve conductance to a predefined metric of conductance versus angularvalve position. The conductance calibration map or function is storedfor use during operation of the valve.

A difference between the measured valve conductance and the predefinedmetric of conductance versus angular valve position can be used indetermining the conductance map or function. During operation, a setpoint angular valve position based on a desired conductance of the valvecan be received. Actual angular valve position of the valve can be setbased on the received set point angular valve position and thedifference between the measured valve conductance and the predefinedmetric of conductance versus angular valve position. An actual systemconductance and a difference between the actual system conductance and areference system conductance for the system can be determined. Adiagnostic indication of a fault in the system can be generated based onthe actual angular valve position of the valve and the differencebetween the actual system conductance and the reference systemconductance for the system. If the actual angular valve position isrelatively low and the actual system conductance is greater than thereference system conductance, in a low-conductance valve, the diagnosticindication can be that a flapper seal of the low-conductance valve isworn. If the actual angular valve position is relatively low and theactual system conductance is less than the reference system conductance,in a non-sealing valve, the diagnostic indication can be that depositionby-products have accumulated on at least one of a valve wall and aflapper of the valve. The relatively low angular valve position can bebelow 20 degrees. If the actual angular valve position is relativelyhigh and the actual system conductance is less than the reference systemconductance, in a low-conductance valve, the diagnostic indication canbe at least one of an at least partial blockage in a conduit of thesystem and degradation of a pump in the system. If the actual angularvalve position is relatively high and the actual system conductance isless than the reference system conductance, in a non-sealing valve, thediagnostic indication can be at least one of an at least partialblockage in a conduit of the system and degradation of a pump in thesystem. The relatively high angular valve position can be greater than50 degrees.

According to another aspect, a method for providing a diagnosticindication in a vacuum system using a valve is provided. According tothe method, a set point angular valve position based on a desiredconductance of the valve is received. An actual angular valve positionof the valve is set based on the received set point angular valveposition and a difference between the measured valve conductance and apredefined metric of conductance versus angular valve position. Anactual system conductance and a difference between the actual systemconductance and a reference system conductance for the system aredetermined. A diagnostic indication of a fault in the system isgenerated based on the actual angular valve position of the valve andthe difference between the actual system conductance and the referencesystem conductance for the system.

If the actual angular valve position is relatively low and the actualsystem conductance is greater than the reference system conductance, ina low-conductance valve, the diagnostic indication can be that a flapperseal of the low-conductance valve is worn. If the actual angular valveposition is relatively low and the actual system conductance is lessthan the reference system conductance, in a non-sealing valve, thediagnostic indication can be that deposition by-products haveaccumulated on at least one of a valve wall and a flapper of the valve.The relatively low angular valve position can be below 20 degrees. Ifthe actual angular valve position is relatively high and the actualsystem conductance is less than the reference system conductance, in alow-conductance valve, the diagnostic indication can be at least one ofan at least partial blockage in a conduit of the system and degradationof a pump in the system. If the actual angular valve position isrelatively high and the actual system conductance is less than thereference system conductance, in a non-sealing valve, the diagnosticindication can be at least one of an at least partial blockage in aconduit of the system and degradation of a pump in the system. Therelatively high angular valve position can be greater than 50 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is further described in the detailed descriptionwhich follows, in reference to the noted plurality of drawings by way ofnon-limiting examples of embodiments of the present disclosure, in whichlike reference numerals represent similar parts throughout the severalviews of the drawings.

FIG. 1 includes a graph of conductance versus valve position for severalsimilar valves.

FIG. 2 includes a schematic block diagram of a processing system,according to an exemplary embodiment.

FIG. 3A includes a schematic diagram of a valve assembly, according toan exemplary embodiment.

FIG. 3B includes a schematic side view of the valve assembly of FIG. 3A,according to an exemplary embodiment.

FIG. 4 includes a graph of conductance versus shaft position for aflapper valve assembly, according to an exemplary embodiment.

FIG. 5 includes a table corresponding to the graph of FIG. 4.

FIG. 6 includes a graph of conductance versus flapper position in anexemplary low-conductance flapper valve, illustrating the case of a wornflapper seal.

FIG. 7 includes a graph of conductance versus flapper position in anexemplary non-sealing flapper valve, illustrating the case ofaccumulation of deposits on the valve body wall or flapper.

FIG. 8 includes a graph of conductance versus flapper position in anexemplary low-conductance flapper valve, illustrating the case ofblockage in a pumping line or pump degradation.

FIG. 9 includes a graph of conductance versus flapper position in anexemplary non-sealing flapper valve, illustrating the case of blockagein a pumping line or pump degradation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments described herein provide for valve-to-valve repeatability ofconductance versus commanded valve, e.g., flapper, position, regardlesswhether the commanded position is externally or internally sourced,e.g., during closed-loop pressure control. The embodiments supportchamber matching and copy-exact requirements, because each valveprovides the same performance as a function of the command provided tothe valve.

According to some exemplary embodiments, a method for calibrating avalve includes measuring conductance of the valve as a function of valveposition and determining a conductance calibration map or function forthe valve by comparing the measured valve conductance to a predefinedmetric of conductance versus valve position. The method also includesstoring the conductance map or function for use during operation of thevalve.

Fluid conductance is a measure of how effectively a fluid moves througha structure or substance. In a vacuum system, the conductance (C) of afluid through a pipe or conduit is determined by the relationship:

$\begin{matrix}{{C = \frac{Q}{\left( {P_{1} - P_{2}} \right)}};} & (1)\end{matrix}$

where Q is the total mass flow of the fluid through the conduit, P₁ isthe pressure upstream, and P₂ is the pressure downstream.

Conductance of a valve is typically controlled by changing the valveopening between open and closed positions. Valve performance istypically reported by manufacturers based on nominal, minimum, andmaximum expected performance. However, actual conductance of a valve canvary widely between different valves. Many properties of a valve, otherthan the degree to which it is open or closed, affect the actualconductance performance. For example, mechanical tolerances ofcomponents and variation in assembly of the components can contributesignificantly to the variation in conductance of one valve relative toanother. While parts may be selected based on precise measurementspecifications and assembly can be customized to achieve exactingtolerances, it is impractical to do so in a production environment.

FIG. 1 is a plot of conductance versus valve position for severalsimilar valves. The Y-Axis is in units of standard cubic centimeters permilliTorr, corresponding to a pressure difference between an upstreamlocation and downstream location relative to the valve. The X-Axis is inunits of percent openness of the valve, varying between 0% open, i.e.,closed, and 100% open. Curve 104 is the maximum expected conductance ofa typical valve, and curve 108 is the minimum expected conductance ofthe valve. Curve 116 is the conductance for an exemplary valve in abatch of produced valves, and curve 112 depicts typical conductanceperformance for valves in the batch.

Semiconductor manufacturers often have multiple processing systems,i.e., tools, which perform the same function. They expect each of thesystems to operate in the same manner with minimal calibration or setup,particularly at initial tool installation and commissioning. Forexample, the manufacturers expect to be able to control the conductanceof a valve using the same process recipes without having to calibrateeach valve during installation or a service interval. Furthermore,manufacturers expect that each valve provide the same conductance for aspecified, commanded or reported position. By way of example, thepossible variation in conductance between a maximum conductance (curve104) and minimum conductance (curve 108) is larger than desired for manyapplications. In general, it is desirable for each valve to operate withthe same conductance, e.g., conductance curve 116, as a function of thecommanded or reported position of the valve, i.e., % open in thisinstance. Embodiments described herein provide methods by which eachvalve provides a known conductance in response to a commanded position.

FIG. 2 includes a schematic block diagram of a processing system 200,according to an exemplary embodiment. The processing system 200 includesa process chamber 230 including a conduit 204 coupled to an output ofprocess chamber 230. System 200 also includes a valve assembly 212coupled to an outlet 206 of conduit 204. Valve assembly 212 is alsocoupled to an inlet 210 of a second conduit 208. System 200 alsoincludes a pump 224 coupled to second conduit 208. Pump 224 draws fluidfrom conduit 208 to create a pressure difference between a locationupstream 214 of valve assembly 212 and a location downstream 218 ofvalve assembly 212.

System 200 also includes an actuator 216 operatively connected to valveassembly 212. Actuator 216 controls the operation of valve assembly 212to vary, for example, the flow of fluid through valve assembly 212 fromconduit 204 to conduit 208. In some embodiments, valve assembly 212includes a butterfly valve, and actuator 216 changes the position of aflapper in valve assembly 212 relative to the passageway through valveassembly 212. In this manner, actuator 216 affects the conductance ofvalve assembly 212 by altering the degree to which the valve isopen/closed. System 200 may also include a valve position sensor 220,e.g., an optical or mechanical encoder, which measures the position ofthe flapper as it changes during operation.

FIGS. 3A and 3B are schematic illustrations of a valve assembly 300according to an illustrative embodiment. The valve assembly 300 is aflapper valve assembly and includes a flapper 304. The flapper 304 issecured to the valve assembly 300 by a rotatable valve shaft 308 thatextends laterally across a passageway 312 of the valve assembly 300.Rotation of the valve shaft 308 is shown by dashed arrow 316. Rotationof the valve shaft 308 by an actuator, e.g., actuator 216 of FIG. 2,controls the position of flapper 304 with respect to passageway 312 ofvalve assembly 300. The conductance of valve assembly 300 is controlledby varying the position of flapper 304 between open and closed positions(shown as 100% closed in FIG. 3B).

Referring to FIG. 2, system 200 also includes a control system 228operatively connected to actuator 216. Control system 228 providessignals to actuator 216 and receives various input signals. Controlsystem 228 controls the operation of actuator 216 to control valveassembly 212. Control system 228 includes a motion controller 232 and,optionally, a pressure controller 236. In one embodiment, motioncontroller 232 receives various signals and information and outputsvarious signals and information, and outputs motion control signals toactuator 216. Optional pressure controller 236 is used in someembodiments with motion controller 232 to calculate control signals tobe provided to actuator 216 to control the pressure in process chamber230 by varying the position of the flapper in valve assembly 212. Thepressure can be measured using, for example, a pressure transducer 240coupled to process chamber 230.

In some implementations, a valve assembly, e.g., valve assembly 212, isused to control the conductance of a gas exiting processing chamber 230.The gas travels along conduit 204 and through valve assembly 212. Thegas then travels through conduit 208 to a reclaim system 256 for safedisposal. A command set point 244 (position set point in thisembodiment) is provided to control system 228. Position set point 244 isthe desired position of the flapper in valve assembly 212 relative tothe passageway passing through valve assembly 212. Position s 244 istypically predetermined for a specific set of processing steps for whichprocessing chamber 230 is intended so that a specific flow conductanceis achieved. In some embodiments, position set point 244 is a 0-10 voltDC analog signal proportional to the desired flapper valve position;with 0 volts corresponding to fully closed and 10 volts corresponding tofully open. Alternative signals are used in alternative embodiments. Forexample, in some embodiments, the signal is a digital signal with valuesproportional to the desired flapper position, or a digital signal thatthe control system uses to increment or decrement the position of theflapper relative to the passageway.

In operation, gas is provided to process chamber 230 via gas inlet 252,and motion controller 232 of control system 228 receives position setpoint 244 and compares it to the actual position of the flapper in valveassembly 212. A signal 260 corresponding to the actual position of theflapper is provided to control system 228 by valve position sensor 220,although in some embodiments the actual position may be derived fromprevious (open loop) position commands provided by the motion controllerto the actuator. Motion controller 232 calculates the error betweenposition set point 244 and actual position signal 260. Motion controller232 then outputs a command signal to actuator 216 to change the flapperposition until the error is zero (or below a desired threshold). Motioncontroller 232 outputs a signal that has the characteristics desired forthe movement of the flapper, e.g., flapper position, speed, overshoot,etc.

Valve assembly 212 may not provide the desired valve conductance afterachieving the position corresponding to the desired position set point244 because of variations in the manufacturing of each valve assembly.This may also be due to system usage and wear factors, such asaccumulation of deposition by-products on various components of system200, such as chamber 230, pump 224, conduits/lines 204, 208, valve bodyand/or flapper; worn flapper seals; blockage in conduits/lines 204, 208;and/or degradation of pump 224. The variations in the valve assemblyresult in variations in the conductance of valve assembly 212.Therefore, it is desirable for control system 228 to modify position setpoint 244 so that the signals provided to actuator 216 by control system228 account for the variation in the conductance of valve assembly 212.

FIG. 4 includes a graph of conductance versus shaft position for aflapper valve assembly, according to an exemplary embodiment. The Y-axisis conductance and the X-axis is the shaft position for positionsranging from 0% (fully closed) to 100% (fully open). Curve 404 is thedesired conductance of the valves as a function of shaft position. Eachvalve does not provide this specific conductance performance because ofthe variations described herein. Curve 408 is the conductance of aspecific valve which does not match the desired conductance shown bycurve 404.

FIG. 5 is a table 500 corresponding to the plot of FIG. 4. Column A oftable 500 is the shaft position (only a portion of the values areprovided for clarity of illustration purposes). Values are provided from0% open (completely closed) to 35% open and 95% open to 100% open(completely open). Column B of the table 500 is the conductance for thedesired performance of the valves (corresponding to curve 404 of FIG.4), also referred to as the “golden unit.” Column C of the table 500 isthe conductance for the performance of the specific valve (correspondingto curve 408 of FIG. 4).

By way of example, if the specific valve was commanded to a shaftposition of 10% open (arrow 504) it would provide a conductance of 1.02(column C, arrow 512), not the desired conductance of 10.02 (column B,arrow 508). Therefore, in order for valve assembly 212 to provide thedesired conductance of 10.02, control system 228 must output a differentsignal to actuator 216 so that the valve position is commanded to be ata different valve position than the 10%. Therefore, actuator 216 mustmove the valve position of the specific valve to approximately 31.62(arrow 516) to achieve a conductance of 10.02 for the specific valve.The values in column D of table 500 (conductance calibration factors)are the positions at which actuator 216 must place valve assembly 212 sovalve assembly 212 provides the desired conductance of curve 404 of FIG.4. In some embodiments, the values in column D are stored in a look-uptable in control system 228, and control system 228 outputs a signal toactuator 216 to achieve that valve position in valve assembly 212 inresponse to position set point 244 provided by a user.

In this embodiment, control system 228 outputs various signals,including actual valve position 264 (the same as position signal 260)and a conductance match position signal 268. In some exemplaryembodiments, conductance match position signal 268 is equal toconductance set point 244. Hence, the approach of the present disclosuresatisfies end-user need to have a known and repeatable position outputvariable versus the actual conductance a valve is producing. In the casein which the valve is providing closed-loop pressure control, theend-user is typically monitoring the reported position from the valve toenable controls, such as, for example, well-known SPC controls,associated with valves manufactured and sold by SPC Company of Torrance,Calif., USA. In contrast, traditional valves typically only report theactual shaft position of the valve's flapper. The conductance matchposition signal 268 of the exemplary embodiments is generated by sensingthe actual shaft position, which is known from the motion control systembeing run. From the internal calibration data described herein, theactual conductance being provided by the valve is determined. The valvereferences the stored reference table of a “golden” valve's conductanceversus position and reports the conductance match position inconductance match position signal 268 as the position at which the“golden” valve would have produced the conductance the valve isproviding at that instant in time.

According to exemplary embodiments, when the valve is used as a positioncontroller, conductance match signal 268 relates to a conductance matchposition equal to conductance set point 244. When the valve is used as apressure controller, conductance match position is not equal toconductance set point 244, since conductance set point 244 in this caseis a pressure set point command. Instead, in this case, conductancematch position signal 268 is generated according to the approachdescribed above in detail.

The values in column D could, alternatively, be stored in memory, e.g.,in a look-up table, in actuator 216 or valve assembly 212 and beconfigured to correct the operation of the valve in response to commandset point 244. In some embodiments, an equation is generated thatapproximates the values in column D as a function of commanded set point244 values so no look-up table is required. Rather, control system 228determines what signal to provide to actuator 216 based on the equationwhich is a function of command set point value 244. The equation may begenerated by, for example, interpolation or curve fit techniques.

Column E of table 500 of FIG. 5 is the position the golden unit would beat to produce the same conductance as the specific valve for a givenshaft position. If optional pressure controller 236 is active and theshaft position of valve assembly 212 is modified during closed-loopcontrol, column E is used to output the equivalent position at which the“golden” valve would generate the actual conductance being delivered bythe valve.

As noted above, in processing systems such as those described above indetail, various factors can cause degradation in system performance overtime. For example, in deposition tools, deposition by-products can buildup in the valve and/or in the pumping line, i.e., plumbing/conduits.This build-up can result in reduced pumping line diameter and/or pumpperformance and can change the fluid conductance of one or morecomponents of the vacuum system; it can also result in reduced pumpingspeed. In response to this degradation, in a non-sealing valve, thevalve can compensate by setting to a larger valve opening position.Also, in a non-sealing valve, this deposition build-up can reduce a gapbetween the flapper and the walls of the valve bore or flow passage,thus reducing the valve conductance, in some cases, to values near zeroconductance. In this case, the valve can compensate by closing less,i.e., by setting to a smaller valve angle. In the case of a sealingvalve, where a flexible seal is provided at the outer edge of theflapper between the flapper and the walls of the valve body bore orpassage can wear over time, which can also alter the conductanceperformance of the vacuum system. In this case, the deposition build-upand/or valve seal wear can prevent the valve from reaching zeroconductance at normal valve angle settings. In this case, the valve cancompensate by closing more, i.e., by setting a smaller valve angle.Therefore, in accordance with the present disclosure, in all of thesecases, the valve position can be correlated to a degree of degradationin one or more components of the system.

According to some exemplary embodiments, conductance match positionsignal 268 is used as a position reporting technique which allows endusers to use throttle valve position as a predictive diagnostic variablefor chamber matching and fault detection and classification of otherfaulty components. This approach satisfies commonly expressed end-userneed to have a known and repeatable position output variable, as opposedto the actual conductance a valve is producing.

Another useful output is “% Conductance.” This variable would be the N₂equivalent conductance (Us) produced by the valve at each position undera specific set of test conditions. The variable % Conductance is anormalized output relative to a standard gas, e.g., N₂, under specifiedconditions. As an example, for a given valve size, the 100% openconductance for N₂ may be 100 l/s. At 80% open, it may be 90 l/s, and soforth. In this illustrative example, when the valve is 100% openphysically and providing 100 l/s conductance, the “% Conductance” outputwould be 100%. When the valve is 80% open physically and providing 90l/s, the “% Conductance” output would be 90%. The reason it is expressedas “% Conductance” and not just “Conductance” is that end users can usethe valve with many different gases and gas mixes, and the measuredconductance is a function of gas type. Thus, generating an output as anabsolute unit (Us) is avoided in favor of the normalized “%Conductance.” This characterization provides the user with atransferable repeatable standard by which to validate that the valve isproviding known calibrated performance. This conductance may be ofinterest as a primary variable, but there will still be a valve-to-valvevariability in conductance versus position. On the other hand,conductance versus conductance match position will have very tightvalve-to-valve repeatability.

The more typical position reporting variables of “step counts basedposition” and “encoder based position” are available from the valve.This allows end users to monitor for second-order dependencies (if theyexist) of actual shaft position versus conductance. However, the primarybenefit of first-order valve-to-valve repeatability for reportedposition versus conductance will be satisfied via conductance matchposition described above.

The pressure dynamics in the downstream pressure control systems can bedescribed as:

$\begin{matrix}{{{V_{chamber}\frac{{dP}_{chamber}}{dt}} = {Q_{inlet} - {S_{system} \cdot \left( {P_{chamber} - P_{pump}} \right)}}};} & (2)\end{matrix}$

where:V_(chamber)—chamber volumeP_(chamber): pressure inside the chamberP_(pump): pressure at pump inputQ_(inlet): inlet gas flowS_(system): combined system conductance.

Under normal circumstances, the pressure at the pump is substantiallylower than the controlled pressure inside the chamber and thus can beignored.

The combined system conductance S_(system) can be described as a seriesconnection of individual conductances of the elements comprising thedownstream pressure control system: chamber, valve, foreline (conduit),and pump:

$\begin{matrix}{{S_{system} = \frac{1}{\frac{1}{C_{chamber}} + \frac{1}{C_{foreline}} + \frac{1}{C_{valve}} + \frac{1}{C_{pump}}}},} & (3)\end{matrix}$

where:C_(chamber)—chamber conductanceC_(foreline): foreline conductanceC_(pump): conductance (pumping speed) of pumpC_(valve): throttle valve conductance.The valve conductance C_(valve) is a highly nonlinear function of valveangle θ, variable between 0% open and 100% open:

C_(valve)=f(θ).

For a typical downstream pressure control application, the followingrelationships between various system components will hold true:

Case I: θ≦10% open, i.e., relatively small valve angle. In this case,system conductance is dominated by the valve conductance only, that is:

C_(valve)<<C_(chamber)C_(valve)<<C_(foreline)C_(valve)<<C_(pump)In this case, equation (3) can be re-written as an approximation:S_(system)≈C_(valve)

Considering this relationship, system diagnostics can be performed basedon the knowledge of valve angle and system conductance S_(system), whichis a generally available variable. As a result, in this case of smallvalve angle, any substantial variation of S_(system) can be attributedto a change in valve conductance. Specifically, for a low-conductancethrottle valve (such as F-seal, Q-seal, etc.), the damage or wear of thesealing element will result in higher system conductance, as illustratedin FIG. 6, and can be used for in-situ diagnostics of valve health.

FIG. 6 includes a graph of conductance versus flapper position in anexemplary low-conductance flapper valve, illustrating the case of a wornflapper seal. FIG. 6 illustrates variation of system conductance due towear of flapper seal. FIG. 6 includes an actual system conductanceS_(system) curve 602 and a reference conductance curve 604. Asillustrated in FIG. 6, in the case of a worn flapper seal, the systemconductance S_(system) will be detected to be higher than the expectedreference conductance at small valve opening angles.

For non-sealing valves, the contamination of valve body due to chemicaldeposits during its operation can be detected as a decrease of systemconductance S_(system) compared to the reference values at low openings,as illustrated in FIG. 7. FIG. 7 includes a graph of conductance versusflapper position in an exemplary non-sealing flapper valve, illustratingthe case of accumulation of deposits on the valve body wall or flapper.FIG. 7 illustrates variation of system conductance due to contaminationof non-sealing valve flapper and body. FIG. 7 includes an actual systemconductance S_(system) curve 608 and a reference conductance curve 606.As illustrated in FIG. 7, in the case of accumulation of deposits on thevalve body wall or flapper in a non-sealing valve, the systemconductance S_(system) will be detected to be lower than the expectedreference conductance at small valve opening angles.

Case II: θ≧60% open, i.e., relatively large valve opening. In this case,foreline, i.e., plumbing (conduit/pipe), conductance and pumpconductance are much smaller than the valve conductance and the chamberconductance. System conductance is dominated by the foreline (plumbing,conduit/pipe) conductance and pump conductance. In this case, equation(3) can be written as the approximation:

$S_{system} \approx \frac{1}{\frac{1}{C_{plumbing}} + \frac{1}{C_{pump}}}$

The effect of the seal is negligible at large valve openings. For bothlow-conductance and non-sealing butterfly valves, the reduction in themeasured system conductance can be attributed to the degradation of pumpperformance or to blockage in plumbing, i.e., conduit/pipe, asillustrated in FIGS. 8 and 9.

FIG. 8 includes a graph of conductance versus flapper position in anexemplary low-conductance flapper valve, illustrating the case ofblockage in a plumbing line, i.e., conduit/pipe or pump degradation.FIG. 8 illustrates change in system conductance due to line blockage orpump degradation in a low-conductance valve. FIG. 8 includes an actualsystem conductance S_(system) curve 612 and a reference conductancecurve 610. As illustrated in FIG. 8, in the case of line blockage orpump degradation in a low-conductance valve, the system conductanceS_(system) will be detected to be lower than the expected referenceconductance at relatively large valve opening angles.

FIG. 9 includes a graph of conductance versus flapper position in anexemplary non-sealing flapper valve, illustrating the case of blockagein a pumping line or pump degradation. FIG. 9 illustrates change insystem conductance due to line blockage or pump degradation in anon-sealing valve. FIG. 9 includes an actual system conductanceS_(system) curve 616 and a reference conductance curve 614. Asillustrated in FIG. 9, in the case of line blockage or pump degradationin a non-sealing valve, the system conductance S_(system) will bedetected to be lower than the expected reference conductance atrelatively large valve opening angles.

Thus, in general, these diagnostics allow an end user, by observingwhich part of the conductance curve is changing, to conclude faults suchas valve contamination, flapper seal wear, foreline blockage, and/orpump degradation.

In some exemplary embodiments, an implementation will utilize recipetimemark triggers that will be coordinated with the tool operation asfollows:

-   -   Tool runs baseline process.    -   I/O with valve accepts an input that marks timemark triggers,        i.e., RecordMark1, RecordMark2    -   At each mark, the valve records and stores in memory its        position, recorded pressure, and internally estimated process        parameters (gas flow)    -   During wafer production, the valve accepts a different trigger        from the tool, that indicates that the recipe is passing through        the same original mark points: i.e. ReadMark1, ReadMark2    -   At each mark point, the valve applies logic to determine if the        conductance curve S_(system) has shifted to the point where it        passes some threshold. The valve will then issue a warning back        to the tool with some indications as to the change, and likely        causes of the change.

In this exemplary embodiment, the details of the communication formatbetween the tool and the valve can be as shown in Table 1.

TABLE 1 Proposed commands and interface to tool Command DirectionFunction Record Mark_n Tool to Valve Valve records pressure controlconditions during “Process of Record” or reference conditions at aparticular recipe step. ReadMark n Tool to Valve Request for valve tooutput diagnostics at this point in recipe Conductance Delta n Valve toTool quantitative output of (response to a Read Mark n) deviation fromactual conductance to that recorded during Process of Record AverageConductance Delta Valve to Tool (response to a quantitative output of(n) Read Mark n) deviation from actual conductance to that recordedduring Process of Record, but averaged over multiple (i) samples atrecipe step n Standard Deviation Valve to Tool (response to a Read Markn) Diagnostic Output Valve to Tool (response to a One of several status:Read Mark n) a. Normal b. System Conductance degrading (conductance athigh valve position is reduced) c. Flapper Gap reduced d. Fsealworn/failed e. Pump speed degrading f. Buildup in valve reducing systemconductance g. Unknown

According to some exemplary embodiments, another enhancement of theimplementation includes the exchange of gas information between the tooland the valve. This allows for the use of a three-dimensional systemconductance table with conductance being a nonlinear function of valveposition and gas composition, that is, S_(system)=f(θ, gas composition).

According to some exemplary embodiments, yet another enhancement of thediagnostic approach described herein in detail utilizes results from theuse of both upstream and downstream pressure information, denoted asP_(chamber) and P_(pump) in equation (2) above. An effective placementof the upstream transducer is immediately at the valve inlet and of thedownstream transducer is at the valve outlet. This transducer placementwill provide further differentiation between clogging the upstreamplumbing versus downstream plumbing and pump degradation.

According to some exemplary embodiments, an alternative to the timemarkapproach is to perform a complete system learn routine during the idletime of the tool. This will generate the complete system conductancecurve S_(system) as plotted above. An advantage of this approach is thata more continuous curve compared to specific operating points obtainedusing the timemark approach.

In this application, including the definitions below, the term ‘module’or the term ‘controller’ may be replaced with the term ‘circuit.’ Theterm ‘module’ may refer to, be part of, or include: an ApplicationSpecific Integrated Circuit (ASIC); a digital, analog, or mixedanalog/digital discrete circuit; a digital, analog, or mixedanalog/digital integrated circuit; a combinational logic circuit; afield programmable gate array (FPGA); a processor circuit (shared,dedicated, or group) that executes code; a memory circuit (shared,dedicated, or group) that stores code executed by the processor circuit;other suitable hardware components that provide the describedfunctionality; or a combination of some or all of the above, such as ina system-on-chip.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. The term shared processor circuitencompasses a single processor circuit that executes some or all codefrom multiple modules. The term group processor circuit encompasses aprocessor circuit that, in combination with additional processorcircuits, executes some or all code from one or more modules. Referencesto multiple processor circuits encompass multiple processor circuits ondiscrete dies, multiple processor circuits on a single die, multiplecores of a single processor circuit, multiple threads of a singleprocessor circuit, or a combination of the above. The term shared memorycircuit encompasses a single memory circuit that stores some or all codefrom multiple modules. The term group memory circuit encompasses amemory circuit that, in combination with additional memories, storessome or all code from one or more modules.

The term memory circuit is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium may therefore be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible computer-readablemedium are nonvolatile memory circuits (such as a flash memory circuit,an erasable programmable read-only memory circuit, or a mask read-onlymemory circuit), volatile memory circuits (such as a static randomaccess memory circuit or a dynamic random access memory circuit),magnetic storage media (such as an analog or digital magnetic tape or ahard disk drive), and optical storage media (such as a CD, a DVD, or aBlu-ray Disc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks andflowchart elements described above serve as software specifications,which can be translated into the computer programs by the routine workof a skilled technician or programmer.

While the present inventive concept has been particularly shown anddescribed with reference to exemplary embodiments thereof, it will beunderstood by those of ordinary skill in the art that various changes inform and details may be made therein without departing from the spiritand scope of the present inventive concept as defined by the followingclaims.

1. A method for calibrating a valve in a vacuum system, comprising:measuring conductance of the valve as a function of angular valveposition; determining a conductance map or function for the valve bycomparing the measured valve conductance to a predefined metric ofconductance versus angular valve position; and storing the conductancecalibration map or function for use during operation of the valve. 2.The method of claim 1, wherein a difference between the measured valveconductance and the predefined metric of conductance versus angularvalve position is used in determining the conductance map or function.3. The method of claim 2, further comprising, during operation,receiving a set point angular valve position based on a desiredconductance of the valve; and setting actual angular valve position ofthe valve based on the received set point angular valve position and thedifference between the measured valve conductance and the predefinedmetric of conductance versus angular valve position.
 4. The method ofclaim 3, further comprising determining an actual system conductance anddetermining a difference between the actual system conductance and areference system conductance for the system.
 5. The method of claim 4,further comprising generating a diagnostic indication of a fault in thesystem, the diagnostic indication being based on the actual angularvalve position of the valve and the difference between the actual systemconductance and the reference system conductance for the system.
 6. Themethod of claim 5, wherein, if the actual angular valve position isrelatively low and the actual system conductance is greater than thereference system conductance, in a low-conductance valve, the diagnosticindication is that a flapper seal of the low-conductance valve is worn.7. The method of claim 6, wherein the relatively low angular valveposition is below 20 degrees.
 8. The method of claim 5, wherein, if theactual angular valve position is relatively low and the actual systemconductance is less than the reference system conductance, in anon-sealing valve, the diagnostic indication is that depositionby-products have accumulated on at least one of a valve wall and aflapper of the valve.
 9. The method of claim 8, wherein the relativelylow angular valve position is below 20 degrees.
 10. The method of claim5, wherein, if the actual angular valve position is relatively high andthe actual system conductance is less than the reference systemconductance, in a low-conductance valve, the diagnostic indication is atleast one of an at least partial blockage in a conduit of the system anddegradation of a pump in the system.
 11. The method of claim 10, whereinthe relatively high angular valve position is greater than 50 degrees.12. The method of claim 5, wherein, if the actual angular valve positionis relatively high and the actual system conductance is less than thereference system conductance, in a non-sealing valve, the diagnosticindication is at least one of an at least partial blockage in a conduitof the system and degradation of a pump in the system.
 13. The method ofclaim 12, wherein the relatively high angular valve position is greaterthan 50 degrees.
 14. A method for providing a diagnostic indication in avacuum system using a valve, the method comprising: receiving a setpoint angular valve position based on a desired conductance of thevalve; setting actual angular valve position of the valve based on thereceived set point angular valve position and a difference between themeasured valve conductance and a predefined metric of conductance versusangular valve position; determining an actual system conductance;determining a difference between the actual system conductance and areference system conductance for the system; and generating a diagnosticindication of a fault in the system, the diagnostic indication beingbased on the actual angular valve position of the valve and thedifference between the actual system conductance and the referencesystem conductance for the system.
 15. The method of claim 14, wherein,if the actual angular valve position is relatively low and the actualsystem conductance is greater than the reference system conductance, ina low-conductance valve, the diagnostic indication is that a flapperseal of the low-conductance valve is worn.
 16. The method of claim 15,wherein the relatively low angular valve position is below 20 degrees.17. The method of claim 14, wherein, if the actual angular valveposition is relatively low and the actual system conductance is lessthan the reference system conductance, in a non-sealing valve, thediagnostic indication is that deposition by-products have accumulated onat least one of a valve wall and a flapper of the valve.
 18. The methodof claim 17, wherein the relatively low angular valve position is below20 degrees.
 19. The method of claim 14, wherein, if the actual angularvalve position is relatively high and the actual system conductance isless than the reference system conductance, in a low-conductance valve,the diagnostic indication is at least one of an at least partialblockage in a conduit of the system and degradation of a pump in thesystem.
 20. The method of claim 19, wherein the relatively high angularvalve position is greater than 50 degrees.
 21. The method of claim 14,wherein, if the actual angular valve position is relatively high and theactual system conductance is less than the reference system conductance,in a non-sealing valve, the diagnostic indication is at least one of anat least partial blockage in a conduit of the system and degradation ofa pump in the system.
 22. The method of claim 21, wherein the relativelyhigh angular valve position is greater than 50 degrees.